1. Field of the Invention
The present invention relates to a lens holding frame for securing a lens element to a lens base. More particularly, the present invention relates to a lens holding frame for securing a lens element to a lens base in an optical instrument with sufficient tightness easily and exactly.
2. Description Related to the Prior Art
A camera among various types of optical instruments includes a taking lens. To focus an image sharply, the lens must be properly controlled for a position. In the course of manufacturing the camera, it is necessary to position the taking lens in two manners, namely, in a direction along an optical axis of the taking lens, and also in directions vertical to the optical axis. It is known in the art to assemble the taking lens in a shutter unit which accommodates a shutter blade and a mechanism for driving the shutter blade. This is effective in miniaturizing the body of the camera.
In FIG. 4, a shutter unit 61 of a known type is illustrated. A shutter blade is incorporated in the shutter unit 61. An electromagnet in the shutter unit 61 controls operation of opening and shutting the shutter blade. A lens holding chamber 62 is formed in a front wall of the shutter unit 61 in a recessed shape for lens assembling. A lens holding frame 64 is inserted in the lens holding chamber 62. A lens element 63 of a taking lens is retained in the lens element 63. A projection end 64a of the lens holding frame 64 is provided. A reference plane 65 is formed with the shutter unit 61, and is contacted by the projection end 64a, so as to position the lens element 63 in the optical axis direction. Bosses 66 are formed to project from the shutter unit 61. A plate spring 67 is secured to the bosses 66 with screws. Push portions 68 of the plate spring 67 press the lens holding frame 64 toward the reference plane 65. An inner diameter of the lens holding chamber 62 of the shutter unit 61 is greater than an outer diameter of the lens holding frame 64. According to a difference between the diameters, the lens holding frame 64 is shifted in directions vertical to the optical axis, so as to reduce or remove eccentricity of the lens element 63 being positioned. After removing the eccentricity, adhesive agent is applied to suitable portions to fasten the lens holding frame 64 to the shutter unit 61.
However, the above-described known method has a problem. To set the lens holding frame 64 on the reference plane 65 of the shutter unit 61, the plate spring 67 is required. To fasten the plate spring 67 to the shutter unit 61 as a holder for the taking lens, the bosses 66 must be formed to protrude. Therefore, the total number of parts is relatively high and cannot be low for the size reduction. A space for securing the mechanism cannot be reduced.
In view of the foregoing problems, an object of the present invention is to provide a lens holding frame for securing a lens element to a lens base easily, exactly and tightly, and also in a manner allowing easy adjustment of the position of the lens element.
In order to achieve the above and other objects and advantages of this invention, a lens holding frame for securing at least one lens element to a lens base is provided. A holding frame body sandwiches the lens element in cooperation with the lens base. At least two arm portions are formed integrally with the holding frame body, having resiliency, for extending substantially radially from the holding frame body. A retention member retains the arm portions to the lens base, the retention member being secured to the holding frame body with the arm portions kept resiliently deformed toward the lens base.
The holding frame body includes a plate portion disposed over one surface of the lens element. A lens opening is formed in a middle of the plate portion, for passage of light through the lens element. A barrel portion is disposed about a periphery of the lens element.
The arm portions have respectively arm holes, and the retention member is screws inserted through the arm holes, and helically fastened on the lens base.
The holding frame body further includes a flange formed on a periphery of the barrel portion, having the arm portions protruded therefrom. Plural arc-shaped slits are formed between the barrel portion and the flange, positioned to correspond to the arm portions, for facilitating deformation of the arm portions with resiliency.
The lens base is constituted by a plate of a shutter unit, and a recess is formed in the plate, for receiving entry of a portion of the lens element.
Bosses are formed on the lens base, for being inserted in the arm holes, and screw holes are formed in a middle of the bosses for helical engagement of the screws.
The arm holes have a diameter greater than a diameter of the boss for adjustment of a position of the holding frame body relative to the lens base.
The arm portions are attached to the lens base with adhesive agent after the screws are fastened on the bosses.
The plate portion includes a projection, disposed in a circular shape, for contacting the surface of the lens element, to push the lens element to the lens base.
Furthermore, a projection is formed to project from the flange substantially radially. An engagement hole is formed in the projection. A detent is formed with the lens base, for engagement with the engagement hole. At least one positioning pin is disposed to project from the lens base. A positioning arm portion is disposed to project from the flange. At least one positioning hole is formed in the positioning arm portion, for being fitted on the positioning pin.
In a preferred embodiment, the lens base is disposed behind the lens element, and the holding frame body is disposed in front of the lens element.
The screws include a threaded portion for helical engagement with a receiving hole formed in the lens base. A head portion is formed on a front end of the threaded portion with a greater head diameter that is greater than a diameter of the arm hole, for pushing the arm portion toward the lens base in the helical engagement of the threaded portion.
The positioning arm portion projects opposite to the projection of the flange with reference to the optical axis of the lens element.